The invention relates to a wet electrophotographic copying apparatus of the so-called visual image transfer type.
Referring to FIG. 1, which illustrates a typical example of a conventional wet electrophotographic copying apparatus of the type described, it essentially comprises a so-called photosensor drum 1, such as an electrically conductive drum on the periphery of which a layer of photoconductive material is disposed; a series of discrete processing units located along the periphery of the drum, including a corona discharge changer C1; an exposure optical system m1, m2, m3 and m4; a wet developing unit 2; a transfer 3 for transferring a visual image onto a recording sheet S; an a.c. corona charger C2 for removing the electric charge on the surface of the photosensor drum 1; a quenching lamp 5 for removing the residual charge within the layer of photoconductive material; a cleaning blade 6; an original receptacle 7 for carrying an original O thereon; and a light source 8 for illuminating the original.
With the apparatus described, a copying operation proceeds as follows: Initially, the photosensor drum 1 is rotated in the counterclockwise direction, and its surface is uniformly charged by the charger C1. Then the original receptacle 7 having an original O placed thereon is moved in the direction indicated by an arrow to be illuminated by the light from the light source 8, whereupon the reflected light from the original O is conveyed by the stationary optical system m1, m2, m3 and m4 onto the uniformly charged surface of the photosensor drum 1, thereby focussing an image corresponding to the original O thereon. In this manner, an electrostatic latent image is formed on the surface of the drum 1 in conformity to the original O. The latent image is converted into a visual image by a supply of a developing solution thereto at the wet developing unit 2. Subsequently, the visual image is transferred onto a recording sheet S at the transfer unit 3, thus providing a copy sheet. Subsequent to the transfer of the visual image onto the recording sheet S, the electric charge remaining on the surface of the photosensor drum 1 is removed by the a.c. corona charger C2, and the charge remaining within the photoconductive layer is removed by the quenching lamp 5.
Of primary importance in the wet electrophotographic apparatus described above is the cleaning step which removes any residual toner on the surface of the photosensor drum 1 after the visual image has been transferred onto the recording sheet S. If the residual toner is allowed to remain on the surface of the drum without removal, it may mar the recording sheet or may cause a degradation in the performance of the photosensor drum during the next copying cycle.
In the electrophotographic copying apparatus described, the residual toner is removed by disposing the edge of the cleaning blade 6 in abutting engagement with the surface of the drum 1. It will be appreciated that, in the copying apparatus of the type described, the location for the cleaning operation is limited to being intermediate the transfer position for the visual image and the position of the charger C1 where renewed charging of the drum surface is effected, so that it follows that the cleaning blade 6 must be located above the developing unit 2. A liquid cleanser is supplied adjacent to the edge of the cleaning blade 6 where it bears against the drum surface in order to avoid accumulation of toner, as separated from the drum surface, adjacent to the edge of the cleaning blade and to prevent the blade 6 from causing damage to the drum surface. Usually, the liquid cleanser comprises the developing solution itself which comprises toner disposed in a carrier liquid such as Isopay (trade name). As a result, in the electrophotographic copying apparatus as shown in FIG. 1, it is necessary to provide means which supplies the liquid cleanser or developing solution adjacent to the cleaning blade 6.
The supply of the liquid cleanser to a location above the transfer unit 3 may cause a flow of the liquid cleanser toward the transfer unit 3, thereby resulting in a disadvantageous marring of the recording sheet S. Additionally, the location of the cleaning station at a position above the charger C1 may also cause a flow of the liquid cleanser toward the latter, again causing a marring thereof or preventing a uniform charging as a result of the liquid flow. In particular, where the exposure optical system comprises a bundle of light focussing glass fibres, the location of the optical system is substantially limited to a region adjacent to the top of the photosensor drum, so that the photosensor drum 1 presents a downwardly declining surface in a region from the cleaning blade 6 to the transfer unit 3, thus requiring provision for preventing a flow of the liquid cleanser into the transfer unit 3. This results in a complex arrangement.